Hitherto, as a diagnostic imaging apparatus effective for the early detection of breast cancer, an X-ray mammography machine is widely known. In an X-ray mammography machine, a breast is compressed and held between an imaging table storing a radiographic detector therein and a compression plate disposed opposite the imaging table, and the breast is irradiated with X rays through the compression plate. In this case, the reason why the breast is compressed with the compression plate is to reduce the thickness of the breast subjected to an imaging operation so that the required radiation dose for the breast can be minimized. Additionally, in order to ensure the safety for a patient and to prevent an excessive burden from being imposed on the patient caused by the compression of the breast, the load applied to the compression plate is measured and displayed. In this case, however, generally, only the load (force) applied to the compression plate is measured and displayed, and the pressure applied to the breast itself on the compression plate is not considered.
PTL 1 discloses the following X-ray mammography machine. By using a two-dimensional pressure sensor provided in an imaging table, the pressure applied to a breast which is being compressed with a compression plate is measured, and a compression pressure distribution is detected and displayed.
Instead of using X rays involving the radiation exposure, a method for obtaining three-dimensional image data indicating an image of a wide area of a breast by using ultrasonic echoes, which is less invasive than X rays, is known. Additionally, the following photoacoustic mammography machine has recently been suggested. A subject (breast) is irradiated with light in an infrared band, such as laser light having a low biological absorption ratio, and photoacoustic waves generated within the subject are detected. Then, three-dimensional image data formed from the detected photoacoustic waves is obtained and displayed. The photoacoustic mammography machine detects photoacoustic waves which are generated as a result of a specific substance within a subject absorbing energy of light irradiated with the subject and forms an image from the generated photoacoustic waves. Examples of a specific substance within a subject are glucose and hemoglobin contained in the blood. In the photoacoustic mammography machine, the blood distribution within a subject and hemoglobin concentration distribution within the blood may be formed into images. Moreover, as a result of detecting photoacoustic waves generated from a subject irradiated with light having a different wavelength, oxyhemoglobin (oxidized hemoglobin) may be formed into an image. In a known X-ray mammography machine, generally, the X-ray transmittance ratios obtained due to the difference in the tissue density of a subject are formed into an image of a subject internal structure. In contrast, a photoacoustic mammography machine is capable of estimating the density and blood oxygen of a newborn blood vessel generated around a cancer tissue. Thus, the photoacoustic mammography machine is being expected as a modality that conducts cancer diagnosis with higher precision and higher reliability.
PTL 2 discloses the following photoacoustic mammography machine. In order to allow light to reach a deep level of a subject, the subject is irradiated with light in the state in which the subject is compressed between compression plates, and then, photoacoustic waves generated from the subject are obtained.